1. Field of the Invention
The present invention relates to improvements in an optical scanning device for scanning a subject medium.
2. Description of the Related Art
In recent years, with development of digital techniques and light sources, numerous high performance printing equipment and the like have been developed, wherein a light beam modulated according to image signals scans a subject matter, such as photographic pictures and printed matter (which is hereafter referred to as a scanning subject medium), that is sensitive to light to record an image on a paper. In such a printing equipment, the utilization is made of an optical scanning device to scan a scanning subject medium. This optical scanning device is, for typical example, configured such that a laser beam from a laser diode is repeatedly reflected and deflected by a rotary polygon mirror so as to thereby oscillate along a line on a subject medium
The polygon mirror rotates at a high speed and, in consequence, generates a current of air therearound. In the case where the polygon mirror is installed in a dust proof chamber formed somewhat hermetic or even in the case where the polygon mirror is installed in an open space, The current of air strikes various parts arranged in a disorderly fashion around the polygon mirror and causes turbulence flows of air. The polygon mirror causes momentary rotational speed variations due to the turbulence flows of air, which always provides aggravation of scanning precision. In order to eliminate an occurrence of rotational speed variation of the polygon mirror due to turbulence flows of air, it is thought to disposed the polygon mirror in a spacious place where nothing interrupts a current of air generated by the polygon mirror, however, this is opposed to a recent tendency toward overall compactness of the optical scanning device.
It is an object of the present invention to provide a compact optical scanning device which restrains rotational speed variations of a polygon mirror that is caused due to turbulence of a current of air generated by high speed rotation of the polygon mirror.
The foregoing object of the present invention is accomplished by an optical scanning device for scanning a subject medium with a scanning beam that is oscillated by a polygon mirror along a straight line on the subject medium which is provided with rotational speed variation restraint means comprising a substantially cylindrical partition having a number of corrugations and is placed so as to surround the polygon mirror by the corrugations, thereby restraining momentary rotational speed variations of the polygon mirror.
According to the result of experimental tests on rotational speed variations of the polygon mirror that were made by the inventors of this application, it has been proved that the corrugated cylindrical partition effectively restrains an occurrence of turbulence air flows that is possibly caused by high speed rotation of the polygon mirror.